Group handover with moving cells

ABSTRACT

A wireless communication system using cells to provide wireless access to services, comprising a first base station installed on board a public transportation vehicle to provide a moving cell, and a second base station installed at a stop at which users enter or leave the vehicle, to provide a fixed cell. A central controller guides handovers of users entering or leaving the vehicle. The first and second base stations to provide data concerning users to the central controller, and the central controller, over many journeys of the vehicle, gathers profile data of users based on the data provided by the base stations. As the vehicle approaches a stop, the central controller makes predictions about users likely to enter and leave the vehicle, and, provides guidance to the first and second base stations for performing handovers.

FIELD OF THE INVENTION

This invention generally relates to cellular wireless communicationsystems, more particularly to systems in which at least some of thecells are provided on moving vehicles, and to a handover method in suchsystems.

BACKGROUND OF THE INVENTION

Wireless communication systems are widely known in which subscriberstations communicate wirelessly using cells provided by base stations.As users move around there is a requirement for handover of the usersfrom one cell to another, that is to say from a first base station(source base station) to a second base station (destination basestation).

Current, “4G”, wireless communication systems include systems based onthe set of standards developed by 3GPP and referred to as LTE or LTE-A,in which the users are referred to as UEs (User Equipments) and the basestations as eNBs (enhanced Node Bs). Mobility management functions inLTE networks for UEs in connected mode handle all necessary steps forhandover. These steps include processes that precede the final HOhandover decision on the source network side (control and evaluation ofUE and eNB measurements), preparation of resources on the target networkside, notifying the UE of the new radio resources and finally releasingresources on the source network side. Handover of UEs also involvestransferring, from one eNB to another, all the information related tothe UE, called its “context”.

A typical handover procedure in LTE networks, taken from 3GPP TS36.300,is illustrated in FIG. 7, showing three phases of handover respectivelylabelled “Preparation”, “Execution” and “Completion”, and illustratingthe signalling which occurs between a UE being handed over, source andtarget eNBs, a Mobility Management Entity (MME), and a Serving Gateway(S-GW).

Suppose that a connected-mode UE is connected to a Source eNB providinga serving cell, and can receive at least reference signals from aneighbour cell provided by a Target eNB. In a step 1. “MeasurementControl”, the UE is triggered to send measurement report by the rulesset by system information, specification etc. (see 3GPP TS36.331). In astep 2. “Measurement Reports”, UE performs measurements of attributes ofthe serving and neighbour cells. Step 3 “HO decision” is for Source eNBto make a decision based on measurement report and RRM information tohand over the UE. Then, (4. “Handover Request”) the Source eNB issues ahandover request to the Target eNB, passing necessary information toprepare the handover at the target side. In a step 5. “AdmissionControl”, admission control may be performed by the Target eNB todetermine whether or not it agrees to accept the UE. Then (6. “HandoverRequest Ack.”) the Target eNB 11 prepares the HO and sends the handoverrequest Ack. to the Source eNB, in which a handover command is includedfor the Source eNB to forward the command in the form of a messagelabelled “7. RRC Conn. Reconf.mobilityControlinfo”, to instruct the UEto connect to the target cell.

Several necessary steps are performed on the network side to ensure alossless user plane path switch, in other words minimum interruption inthe data packets being transmitted to or from the UE. These include astep 8. “SN Status Transfer” by which the Source eNB informs the TargeteNB of the Sequence Number (SN) up to which it has successfullydelivered data packets, in order for the Target eNB to know at whichpacket to start transmission.

After receiving the handover command, UE performs synchronisation toTarget eNB (9. “Synchronization”) and accesses the target cell. TheTarget eNB responds (10. “UL Allocation+TA for UE”) with an uplinkallocation and timing advance. When the UE has successfully accessed thetarget cell, the UE sends a message (11. “RRC Connection ReconfigurationComplete”) to the Target eNB to confirm the completion of handover.

The subsequent steps 12.-15. in FIG. 7 can be summarised as a user planepath switch, which changes the DL user plane data delivery path from thepath: S-GW->Source eNB to: S-GW->Target eNB. Finally, the MME confirms(16. Path Switch Req. Ack) the handover and the Target eNB then sends amessage (17. “UE Context Release”) to instruct the Source eNB to releasethe resources previously allocated to the handed-over UE.

As will be understood, the above handover process is considerablyinvolved and requires a considerable amount of signalling to beexchanged among the UE, eNBs, MME and S-GW. FIG. 7 illustrates ahandover of a single UE but the same eNBs may need to hand over multipleUEs at the same time. This is possible if the required controlsignalling is carried in different radio resources for each UE.Generally, handovers are conducted on a “first come, first served”basis.

Next generation wireless communications systems such as so-called “5G”aim to offer improved services to the user compared to the existingsystems. These systems are expected to offer high data rate services forthe processing and transmission of a wide range of information, such asvoice, video and IP multimedia data.

To meet this expectation, 5G networks will employ “small cells” as anindispensable part of the 5G landscape. Small cells have already beenproposed for use in fixed locations in homes, offices and public spacesas an addition to conventional, “macro” cells, for example to fill incoverage holes in the macro cell network and provide localised capacityhotspots. However, 5G networks are also likely to include small cellsmounted on moving public transportation vehicles to enhance thecoverage, capacity and service quality for the in-vehicle mobile usersand to reduce the environmental impact of mobile communication systemsby deploying wireless access nodes close to where users are. Such smallcells mounted inside vehicles will henceforth be referred to as “movingcells”. Both fixed and moving small cells can be managed in anoperator-neutral way (Small Cells as a Service, SCaaS), to avoidunnecessary duplication of hardware.

Taking a bus as an example of a moving public transportation vehicle,user equipments (UEs) inside the bus will connect to an inside basestation/access point instead of to outside macro- or small cells, and atransceiver will be placed outside the bus for transmitting/receivingdata to/from the macro-cell providing the wireless backhaul to the corenetwork. When stopped at a bus stop, the transceiver may further be ableto co-operate with small cells in the vicinity, such as a small cell ofa femto base station provided at each bus stop. Thus better signalquality and high data rate can be provided to the in-vehicle UEs tosatisfy their needs for various mobile data services including thosehaving rigorous requirements on latency emerging in the 5G era.

There are several issues that need to be addressed for this moving cellscenario, such as the management of handovers that occur when passengersget on/off the bus at bus stops. As will be appreciated from the abovediscussion of a conventional handover, if many users get on or off apublic transportation vehicle at the same time and attempt to performhandover, the result will be a high signalling load on the network andincreased latency experienced by the users.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda wireless communication system using cells to provide wireless accessof users to services, comprising:

-   -   a first base station installed on board a public transportation        vehicle, to provide a moving cell;    -   at least one second base station installed at a stop at which        users enter or leave the vehicle, to provide one or more fixed        cells; and    -   a central controller for guiding handovers of users entering or        leaving the vehicle; wherein the first and second base stations        are arranged to provide data concerning users to the central        controller, and the central controller is arranged to gather        profile data of users based on the data provided by the base        stations, make predictions about which users are likely to enter        and leave the vehicle at the stop, and based on the predictions,        to provide guidance to the first and second base stations for        performing handovers of the users.

Here, “public transportation vehicle” refers to a mode of transport suchas a bus, train or tram carrying several persons each of whom may be auser of the wireless communication system. The “stop” at which usersenter or leave the vehicle may be a bus stop, train station or the like.

Preferably, the central controller is arranged to gather the profiledata of users by recording details provided by the first and second basestations of wireless accesses of each user to the moving cell and/orfixed cells during a plurality of journeys using the publictransportation vehicle (or similar such vehicles). In other words theprofile data is built up over time based on past history of users'journeys. Such details can include:

-   -   at least one identity of the user;    -   the time the user established a connection with the moving or        fixed cells; and    -   the time the user ended the connection with the moving or fixed        cells.

Here, “identity of the user” can include an identifying code of theuser's mobile device, and/or an ID code contained in an RFID (RadioFrequency IDentification) device installed either in the mobile deviceor on the user's person.

Further details recorded by the central controller may includeinformation identifying a service or services which the moving or fixedcells provide to the user.

The guidance provided by the central controller preferably includes anumber of handovers from the moving cell to the fixed cells and from thefixed cells to the moving cell, which the central controller predictswill be needed when users enter and leave the vehicle at the stop.

The guidance provided by the central controller may also include anindication of resources predicted to be freed up from the moving celland the fixed cells as a result of the predicted handovers. The centralcontroller may further provide an indication of which fixed cell isselected as a handover target cell for a user which is leaving thevehicle, and/or an indication of resource allocations predicted to beneeded in the moving cell and the fixed cells after users have enteredand left the vehicle at the stop.

The details provided by the first and second base station preferablyinclude information identifying at least one type of service which themoving or fixed cells provide to the user, in which case, preferably,the central controller is arranged to predict whether the user is likelyto continue to require wireless access to the service after leaving orentering the vehicle, and the indication of resource allocations takesinto account resource demands of the service.

The first base station, installed on board the public transportationvehicle, preferably updates the central controller with the position ofthe public transportation vehicle, so that the central controller isable to provide said guidance prior to the vehicle reaching the stop.

By using the guidance provided by the central controller, the first andsecond base stations may perform the handovers without a need for thehandovers to be triggered by measurement reports from the users.

More particularly, handovers may be performed on the basis of one ormore of:

-   -   guidance from the central controller regarding which users are        predicted to enter or leave the vehicle;    -   recent handovers of other users during the same journey of the        vehicle;    -   past handovers of the same user during earlier journeys on the        vehicle;    -   measurements of the fixed cell by the first base station; and    -   historical measurement reports of the users.

Handovers may be further guided by information gathered by an RFIDreader of the vehicle, if available.

According to a second aspect of the present invention, there is provideda central controller for wireless communication system using cells toprovide wireless access of users to services, the wireless communicationsystem comprising a first base station installed on board a publictransportation vehicle, to provide a moving cell; and at least onesecond base station installed at a stop at which users enter or leavethe vehicle, to provide one or more fixed cells; wherein

-   -   the central controller is arranged to receive data concerning        the users from at least the first base station, gather profile        data of the users based on the data so received, make        predictions about which users are likely to enter and leave the        vehicle at the stop, and based on the predictions, to provide        guidance to the first and second base stations for performing        handovers of the users.

According to a third aspect of the present invention, there is provideda method of controlling a wireless communication system, the wirelesscommunication system using cells to provide wireless access of users toservices and comprising a first base station installed on board a publictransportation vehicle to provide a moving cell and at least one secondbase station installed at a stop at which users enter or leave thevehicle, to provide one or more fixed cells, wherein the methodcomprises steps of:

-   -   receiving data concerning the users from at least the first base        station;    -   gathering profile data of the users based on the data received;    -   making predictions about which users are likely to enter and        leave the vehicle at the stop, and    -   based on the predictions, providing guidance to the first and        second base stations for performing handovers of the users.

According to a further aspect of the present invention, there isprovided software which, when executed by a general-purpose computer,provides the central controller as defined above. Such software may bestored on a computer-readable medium.

Embodiments of the present invention differ from previous proposals inthis area in features including the following.

-   -   Group handover conditions arising in a moving cell are addressed        by making predictions about a group of users, specifically in a        moving cell and by accounting for the bi-directional movement of        users at a bus/train stop.    -   A network oriented solution is proposed, which has a holistic        view of the multiple destination cells based on previously        reported values to determine what level of capacity will be        freed and what level of QoS can be provided.    -   A travel route prediction method is provided, based on the        statistical analysis on the likelihood of a UE getting off at a        certain stop or station when taking a particular route by public        transport, which builds up the UE's travel profile over time        using the UE's connection and disconnection events with the        in-vehicle femtocells of different public transportation        vehicles that the UE take and the route and station information        of different vehicles.    -   The prediction method calculates the likelihood of a UE getting        off at a certain station based on the UE's historical travel        behaviours to predict the travel destination for the UE.    -   The prediction method can use a UE's historical travel data on a        particular journey (e.g., bus route) to predict the likelihood        that the UE gets off at a certain station. That is, a UE's        connection and disconnection events with in-vehicle femtocells        and vehicle route and station information may be employed to        predict the likelihood that the UE gets off at a certain        station.    -   A centralized solution is provided, which can have a holistic        view of available resources from the surrounding fixed cells at        a stop or station. It can be assumed that in a densely deployed        heterogeneous network there are multiple cells that can provide        coverage in the area of the stop or station, and the fixed cells        can be virtual cells.

In general, and unless there is a clear intention to the contrary,features described with respect to one aspect of the invention may beapplied equally and in any combination to any other aspect, even if sucha combination is not explicitly mentioned or described herein.

As is evident from the foregoing, the present invention involves signaltransmissions between a network and terminals in a wirelesscommunication system. In a wireless communication system, typically,wireless access to the network is provided by one or more base stationsor access points. Such a base station may take any form suitable fortransmitting and receiving such signals. It is envisaged that the basestations will typically take the form proposed for implementation in the3GPP LTE and 3GPP LTE-A groups of standards, and may therefore bedescribed as an eNB (eNodeB) (which term also embraces Home eNB or HeNB)as appropriate in different situations. However, subject to thefunctional requirements of the invention, some or all base stations maytake any other form suitable for transmitting and receiving signals fromuser equipments.

Similarly, in the present invention, each terminal may take any formsuitable for transmitting and receiving signals from base stations. Forexample, the subscriber station may be referred to as a user equipment(UE) or mobile station (MS), and may take any suitable fixed-position ormovable form. For the purpose of visualising the invention, it may beconvenient to imagine the terminal as a mobile handset (and in manyinstances at least some of the user equipments will comprise mobilehandsets), however no limitation whatsoever is to be implied from this.In the detailed description which follows, in which embodiments of thepresent invention are described with respect to LTE by way of example,the terminal is referred to as a UE in accordance with usual LTEterminology.

Incidentally, the terms “user”, “commuter” and “passenger” are usedinterchangeably below and refer to users of the wireless communicationnetwork (in other words, users carrying a mobile device which isswitched on). References to users and passengers also include the mobiledevices (terminals) of such users unless otherwise demanded by thecontext.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made, by way of example only, to the accompanying drawingsin which:

FIG. 1 shows a system architecture to which the present invention can beapplied;

FIG. 2 schematically illustrates a central controller employed inembodiments of the present invention;

FIG. 3 schematically shows a history table compiled by the centralcontroller of FIG. 2;

FIG. 4 is a flowchart of steps in a method embodying the presentinvention;

FIG. 5 is a block diagram illustrating an example of a UE 10 (terminal,mobile device) to which the present invention may be applied;

FIG. 6 is a block diagram illustrating an example of a BS/AP 20 to whichthe present invention may be applied; and

FIG. 7 shows a conventional handover procedure in LTE.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described by referringto buses as an example of public transportation vehicles to which thepresent invention can be applied. It will be understood, however, thatthis is merely an example and that the present invention can be appliedto various transportation systems involving users riding in vehicles andentering/leaving the vehicles at predetermined stations or stops. Thisincludes railway and tram services for example.

FIG. 1 shows a system architecture to which the present invention can beapplied. It is assumed that there is a bus B travelling on a route(indicated in part by arrow R) between successive bus stops BS1, BS2.Users getting off the bus B are initially in the vicinity of BS1 or BS2,then may migrate elsewhere for example to a shopping centre SC or alocal store LS.

The bus B is equipped with an in-vehicle femto eNB 10 having an exteriorantenna for wireless communication (indicated at W) with a Macro eNB 11,and within the bus B, the eNB 10 provides a moving femto cell 100 forwireless communication with user devices of users travelling on the bus.The bus may be further equipped with at least one RFID reader forregistering RFID devices as they pass in the vicinity of the reader.When installed on the bus doors, this provides a mechanism for recordingexit and entry of users carrying an RFID tag (for example, installed inthe user device).

The Macro eNB controls a macro cell 110, which for simplicity is assumedto cover the whole geographical area considered in FIG. 1 (in reality ofcourse multiple overlapping macro cells would normally be present). Eachbus stop BS1, BS2 has a bus stop eNB (fixed eNB) 12, each providing atleast one small cell 120 respectively. Users U are waiting at each busstop and, like the users on the bus B, will be using their mobiledevices in general and receiving services via the bus stop eNBs 12. Theshopping centre SC and local store LS likewise each have small cells 130provided by respective fixed eNBs 13, serving users in their vicinity.The fixed eNBs can communicate with a central controller 20 via a fixedline connection denoted F (which could alternatively be a wirelessconnection in some cases). The moving eNB 10 can likewise communicatewith the central controller 20 via wireless communication W with theMacro eNB 11. It is preferable (and assumed here for simplicity) that atleast the small cells (moving and fixed) are operator-neutral, andtherefore available for use by any of the users. The location of thecentral controller is not important but it could, for example, beco-located with a MME.

When the bus B arrives at bus stop BS2 for example, a number of users Uget on/off the vehicle, which generates a large number of handovers ofmobile devices (UEs) of those users, between the moving cell 100 on busB and the outside macro and small cells 110, 120. Such handovers arereferred to in this specification as “group handovers” although, as willbe appreciated by those skilled in the art, the users need to be handedover individually (one by one) in practice, incurring a large signallingoverhead as explained previously with respect to FIG. 7.

This problem becomes more serious especially at main bus stations ortransport hubs where lots of passengers get on/off vehicles. Suchbi-directional group handovers can lead to network congestion anddegradation in users' quality of experience if the sudden surge inhandover traffic cannot be accommodated by the network appropriately, orif the service delays due to handover exceed the tolerance limit of somedelay-sensitive applications.

The traditional way a handover is done is based on UE's measurements onneighbouring cells' signal strength and handover is performed for eachUE individually without considering the overall condition of thenetwork. It is highly likely that UEs' measurements on signal strengthwill be similar to each other upon a bus reaching a bus stop. Thereforethe handover decisions made for the group of UEs on the same bus may bethe same, which will cause some cells in the network to be congestedleading to high dropping call rate and some cells to be leftunderutilized resulting in waste of network resources.

In this scenario, embodiments of the present invention provide aresource management scheme to optimize the handover decisions made for agroup of users that require handover at the same time, to overcome thedrawback of the traditional signal strength-based handover mechanism. Aresource management scheme is proposed that makes handover decisions fora group of users taking into account individuals' requirements on QoS,current context, and a holistic view of the system's traffic flows andavailable resources. The group handover decision making process isperformed pre-emptively on the basis of prediction on the bi-directionalHO traffic upon a bus arriving at a bus stop to improve the handoverefficiency and meet many 5G applications' stringent requirements onlatency.

In other words the present invention takes a group (and bidirectional)approach to managing handovers of individual UEs in order to take anoverall view of what resources will be required, and what resources maybe freed, in the target and source cells.

The focus of the proposed scheme is to consider the handovers when amoving cell arrives at a bus/train stop as a group problem and not asindividual handovers. In this respect, a holistic view of the availableresources is taken at the network controller level, which also considersthe bi-directional flow of the users. However some form ofprioritisation may still be needed in individual handover decisions.Some guidelines for this prioritisation are provided.

The present invention is applicable to public transport vehicles likebuses, trams or trains, which have a pre-defined route, and stops orstations at known locations. The majority of the commuters in thesevehicles are regular users and they have the same get-on and get-offstops. They mostly travel at the busy times for the transport network,and these are the times when the communication networks are also putunder a lot of strain. Some of these users will furthermore be activeusers, in other words, will use their mobile devices for data or voiceservices inside the public transport vehicle and/or while waiting at astop or station; these commuters are a particular target of the presentinvention. We assume the small cells (Femto eNBs) within the vehicles tobe operator neutral, where they support all of the operators' consumersand also provide unlicensed spectrum services like WiFi. At busy timesfor the transport network, there will be multiple commuters getting offfrom the vehicle as well as multiple users getting on, at many of thestops.

Central Controller

FIG. 2 schematically illustrates functional blocks of the centralcontroller shown in FIG. 1. The central controller 20 is connected toreceive data from, and provide instructions to, each of the eNBs (cells)shown in FIG. 1, namely each bus eNB 10 (moving cell), macro eNB 11(macro cell), bus stop eNB 12 and shop eNB 13 (fixed small cells).Although only one of each type of cell is indicated for simplicity, inreality of course the central controller would be connected to many suchcells, and multiple fixed cells may be available in the vicinity of eachbus stop. The geographical coverage of the central controller would be,for example, at least one complete bus route, although it only has tofocus on one public transportation vehicle and one stop (station) at atime. The central controller could potentially cover many publictransportation routes or even an entire transportation network.

The central controller 20 includes a communications module 22, a history& measurement module 24, a prediction module 26, and a handover decision28. The communication module 22 receives data from the eNBs and providesguidance or recommendations to eNBs such as handover decisions andresource allocation requirements. The history & measurement module 24 isresponsible for building up and storing profiles of individual users inthe manner described below. The prediction module 26 makes predictionsof the likely future behaviour of individual users on the basis of thestored profiles and the current location of the bus. The handoverdecision module 28 aggregates the predictions of the prediction module26 to assess how many handovers are likely to be required at each busstop (in both directions: from moving to fixed cell and vice-versa) andcauses the communication module 22 to issue instructions to the relevanteNBs accordingly.

Profiling Users

The first step is to build-up profiles of the users who regularlycommute by bus (in this example). When active users camp onto the Femtocell of the bus B, they can be recognised by their unique user ID. Whenthey move out (leave the bus B), that is registered as well. Activeusers within the vehicle are of particular interest, as handing themover while guaranteeing the QoS levels is the challenge. For theseactive users some profiling of their usage can be conducted. Thein-vehicle Femto cells provide this information to a central controller,where the profiling is carried out by gathering several days' worth ofdata. The same commuters may use different vehicles of the fleet on adaily basis, but all these vehicles will have Femto eNBs connected tothe central controller to provide this information. Similarly there willbe small cells (operator neutral) at the bus/train stops which gathersimilar data and provide it to the central controller.

FIG. 3 illustrates the principle of profiling users based on pastbehaviour. It shows a table representing the kinds of information whichcan be gathered by eNBs and forwarded to the central controller. Thefirst column of the table is a user ID which may be based on any IDavailable to the network, such as a TMSI (Temporary Mobile SubscriberIdentity) of the user's mobile device (UE). Another form of ID which maybe employed during the profiling process (preferably in addition to theTMSI or the like) is an RFID installed in the mobile device. In thisway, profiles can also be associated with the UEs' individual RFIDs inaddition to the ID(s) allocated by the mobile network. The mappingbetween the two types of ID can be based on users' behaviourinformation, such as when the user's UE connects and disconnects withthe in-vehicle eNB, when the user gets on and gets off the bus, and whatmobile services were used during the user's stay on the bus.

The second column identifies the cell (or eNB) to which the user hasconnected in a “session” having the start and end times shown in thethird and fourth columns. During each session, the user may have used atleast one network service such as checking e-mails, watching a videostream or playing an online game. The service(s) consumed during thesession are likewise recorded in the 5^(th) column in the table.

A few example values for part of one morning's activity are shown in thetable. For example, a first user “nnnnn” boards a bus and connects tomoving cell B00001 at 8:25:32 one morning on the way to work. He leavesthe bus at 8:55:13, checking his e-mails during the journey. The sameuser is recorded as then joining a fixed cell S00001 at the bus stopwhere he disembarked from the bus, and continues to browse e-mailsduring a session lasting until 9:20:39 at the bus stop.

Meanwhile, a second user “ppppp” boards the bus for which the movingcell ID is B00001, a few seconds after the first user, and uses thejourney to watch a video stream. She has a longer journey than the firstuser; her session ends at 9:10:45 after which she joins the cell of abus stop whose cell ID is S00002, further along the bus route. Afterleaving the bus, she no longer watches the video but leaves her mobiledevice in an on state (“connected”).

A third user qqqqq joins the bus at the stop where the first user gotoff, and commences to play on online game. He leaves at the next stopwith cell ID S00002 but is not recorded as joining that cell, presumablybecause he has turned off his mobile device (the reason for ending thesession, such as handover or leaving the network, could also berecorded).

It should be noted that the above is only one example and otherpossibilities include adding session details from the macro eNB 11and/or each stop eNB 12 to the table. Further data which could usefullybe recorded by the central controller 20 include signal strengthsmeasured by UEs inside the bus. For practical purposes, the centralcontroller would not have any restrictions on storage capacity and so itwould be feasible to build up profiles for many different users overmonths or even years. To maintain relevance, however, it may bepreferred to give higher weight to more recent data in the profile. Bycontrast, it would not normally be necessary for the eNBs to store userbehaviour data except on a temporary basis pending forwarding to thecentral controller.

It can be seen from the above that the profiling process enables thecentral controller to identify some patterns of commuter behaviour, bothat an individual and on a group level. Particularly on commuterjourneys, users tend to do the same things every working day. Forexample, it may be that user nnnnn always boards a bus at the same stop,usually spends his journey checking e-mails, and likes to stay connectedat the destination bus stop. Meanwhile, another user such as ppppp mightwants to use services whilst on the bus but not at other times. Fromsuch patterns, the central controller can establish the bi-directionalcommuter movement (some getting out and some getting in) at most of thebus stops/stations at busy times.

It will be noted that, for profiling purposes, the identity of themoving cell is of less importance than the identities of the fixedcells. Since different public transportation vehicles will normallyserve the same route, it does not especially matter which specificvehicle is boarded by an individual user. It may therefore be sufficientsimply to distinguish the moving cell as moving rather than fixed, andvehicles serving the same route could be grouped together for profilingpurposes (on the basis of a common bus route number for example). On theother hand, the specific cell IDs of fixed cells available at placeswhere the user enters or leaves the bus are of greater relevance, sincenormally these will stay the same for a given bus stop.

Generally, there will be multiple eNBs (including background Macrocells) available at the stops and the controller will have a holisticview of the available resources in these cells. This provides multipleoptions for the controller to assign resources to each UE. The proposedscheme also provides guidelines to optimize this resource transfer.Although the central controller can only predict each individual'sbehaviour, and each individual may not always act as predicted, theoverall prediction can be accurate enough to be useful for facilitatinghandovers and resource allocation in the moving and fixed eNBs.

Group Handover

When sufficient knowledge about the commuters' UEs has been built up inthe central controller, group handover procedures can be executed. Themain focus of this process is to minimize the handover delays and ensureeach UE is provided the appropriate level of resources to maintain theirQoS.

FIG. 4 is a flow chart of the main steps for the implementation of theproposed Group handover solution.

The process starts at S10.

In step S12, the bus eNB 10 detects that the bus is approaching the nextbus stop. The bus and/or bus eNB may for example be equipped with apositioning system (such as GPS) and a map of the bus stops, to enablethe eNB to know when the next stop is close. If it has not already doneso, the bus eNB 10 supplies the central controller with user IDs of thecurrent active users on the bus.

In step S14, the moving eNB uses its external antenna to makemeasurements on the signal strength of neighbouring cells, such as thefixed cell 120 of bus stop BS2. Alternatively, the central controller 20can make use of historical data for this.

In S16 the moving eNB provides (if necessary) the signal strengthmeasurements to the central controller 20. Meanwhile, the fixed eNB(s)at bus stop BS2 informs the central controller of the number ofpassengers waiting at the bus stop. (For present purposes, “likelypassengers” means users of the wireless communication network waiting atthe bus stop: other users having no active mobile device are of nointerest).

In step S18 the central controller checks the user IDs against itsdatabase of stored profiles. It then predicts, based on the storedprofiles of the users, which users are likely to get on and off the buswhen it stops at the next stop (such as BS2 in FIG. 1). This stepapplies, of course, to users for which a stored profile exists. As forusers for which no profile has yet been stored, these users can behanded over initially in a deterministic manner (waiting for measurementreports from the UE to trigger handover in the conventional way), but aprofile for such users is gradually built up until the aboveprediction-based approach can take over. When the prediction algorithmdecides there is enough prior knowledge with respect to a specific user,it will start including that user in its predictions. Thus, all usersare handled but with a varying degree of reliance upon prediction.

In this way, the central controller 20 predicts how many users areexpected to get off the bus when it reaches BS2 (i.e., disembark) andhow many new passengers will get on (embark).

In S20 the central controller determines how many handovers are likelyto be required as a result of the bidirectional movements predicted inS18. As already mentioned, “group handover” means a set of individualhandovers.

In S22, the central controller 20 informs the relevant eNBs (inparticular the moving eNB 10 and bus stop eNB 12) of the handoverdecisions reached in S22. The central controller does this whilst thebus B is still approaching bus stop BS2, allowing the eNBs to receiveadvance warning of the required handovers and the kinds of resourceallocation to be required.

It should be understood that the above “handover decision” provides nota definite handover instruction, but rather, an indication/guidance forthe involved cells about the potential bi-directional user movementsthat are about to occur. With this information the cells are betterprepared to facilitate incoming active users as they are aware of theresources they will have after the bi-directional user movements. TheeNBs do not necessarily have to follow the recommendation of the centralcontroller with respect to specific UEs.

The guidance from the central controller can be provided when the movingcell enters the cell group (cluster of cells) serving the bus stop. Thisis before the bus/train actually stops, but is in the vicinity of thebus stop. When the moving cell enters the cluster, other Femto cellswill identify it as a neighbour and will request the active users toproduce signal measurement reports on this moving cell, in accordancewith conventional behaviour.

In S24, the source eNBs (namely, moving eNB 10 and bus stop eNB 12)perform the required handovers under guidance of the central controller20. It is not necessary to execute the handovers unconditionally: forexample if a passenger who was expected to get off the bus does not infact do so, the handover can be cancelled for that user. For example,RFID sensors on the bus doors could be used to uniquely identify UEsthat pass by the doors when the doors are open. The identified UE IDscan then be sent to the in-vehicle eNB to allow it to confirm theexecution of HO procedure according to the guidance provided by thecentral controller.

The process ends at S26, starting again when the bus B approaches thenext stop.

Some of the above steps will now be described in more detail.

(i) Prediction of User Behaviour/UE Activity

The profiling of users allows the central controller to predict the userbehaviour, more particularly to predict at which stations a user willget on and get off the vehicle. Also the controller can track the userbehaviour after the handover has occurred, to record for example whetherthe user continues to consume the content or not. This information canbe vital in determining the best handover policy for a group of users.

When a particular public transport vehicle nears a stop/station, thecontroller predicts how many users will get off, with the aid of theuser profiles. The controller also has historical data about whichdestination cells are best suited to provide on-going services to theusers. Of the current active users served by these ‘destination’ cells,the controller predicts who will get on to the arriving vehicle. Thenthe controller alerts both the in-vehicle Femto cell and the fixedSmall/Macro cells serving the bus/train stop about the impending usertransfers. In some cases, there will be multiple logical cells (as withCarrier aggregation in LTE-A) available, in which case the UEs can behanded over to multiple cells, with features like dual connectivity.

(ii) Steps to Speed Up the HO Process

For speed and efficiency, the handovers can be conducted as networkinitiated handovers. This is an alternative to UE measurement basedhandovers. If the serving (moving) cell finds that the measurements aredelayed or there are a larger number of potential handovers than itcould handle through the UE measurement method, it could opt for thismethod. Part of this method is providing the historical measurements (ofthe same location) to the controller or the destination cell: these arethe UE measurements (from inside the vehicle) of the outside fixedcells, prior to handover. As these measurements will be more or less thesame each time, the moving eNB can provide the historical values ascurrent values in situations mentioned above.

A conventional handover, as explained earlier with respect to FIG. 7,requires the source eNB to request UE measurements for the neighbourcells to verify which neighbour cell suits best for handover. The methodof the invention preferably uses measurements taken by the vehicularFemto eNB of the signal strengths of Fixed outside cells, or thehistorical signal strength measurements from the UEs to speed up theprocess. If the controller intends to handover to a Macro cell forexample, the measurements provided by the in vehicle Femto eNB would bevery much similar to the UE measurements themselves, so this could be aneffective replacement. In the case of a fixed small cell in thestation/stop taking over, the historical UE measurements recorded by thecontroller could be used instead. It may also be possible for historicalUE measurement reports to be accumulated and stored locally in thevehicle eNB.

In a bus for example, all of the users leaving the bus at a particularstop will normally leave by the same exit door and then come intocontact with the neighbour cell. Up to this point, they will be servedby the moving cell. It is this measurement (at the exit point) thatmatters, which will be almost the same every time, even if individualusers then disperse and later join different cells. This measurement canbe provided to the controller or the destination cell in advance tospeed up the handover.

Optionally, in some network deployments, the UE measurements could beentirely avoided, if the UEs make a handover which merely repeats thehandover patterns of preceding mobiles (e.g. minutes before) in thislocation, or repeats handover patterns of the same UE on preceding daysassociated with a given location (for example). There may be newspecifications in future, which allow the network to completelycircumvent the UE measurements and reporting procedures for these“repetitive” handovers for which the handover pattern (i.e. thecombination of source and destination cells) is always the same.

It will be noted that there is a risk in this approach of aninappropriate handover which does not necessarily reflect an individualUE's behaviour. However, if this occurs then the handover can bereversed and more appropriate action taken.

Regarding the detailed procedures for actually executing the handover,these can follow the kind of signalling sequence shown in FIG. 7, as itassumed that these procedures will not significantly change in 5Gstandards.

(iii) Accommodating the Bi-Directional Commuter (User) Flow

An important consideration in the present invention is thebi-directional commuter (user) flow at the bus/train stops. Accountingfor this bi-directional flow in a holistic manner can provide moreeffective handover solutions. It enables eNBs to take-up active users(and their load), with the knowledge that there will be a certain amountof offloading (which will again be estimated and provided by thecontroller) occurring imminently.

The holistic view provided by the controller is crucial to make thesebi-directional handovers a success. As noted before, there will bemultiple fixed cell options (including background Macro cells) toaccommodate the active users getting off the vehicle. The users waitingat the bus stop to get onto the vehicle will be connected to thesemultiple cells. Therefore, the central controller (by collectinginformation from a plurality of eNBs) will have a holistic view of thebi-directional flows likely to happen when the vehicle arrives at thestop/station, in a way which is not possible for any of the eNBsindividually. The controller can instruct a certain fixed small cell totake up some load, while providing indications that a certain level ofoff-loading is imminent.

(iv) Criteria for User/Resource Allocation at Handover

Some examples will now be given of criteria which determine (from thecentral controller point of view) to which cell the UE should be handedover and what level of resource allocation will be needed.

As noted before, the handovers of multiple users can be handled inparallel as sufficient signalling channels are available. Most of thedelay occurs in reporting measurements, which the present inventionattempts to circumvent.

The physical handover of each user cannot be delayed, as when the usersmove out of the vehicle, they need to connect to a fixed cell or elsethe connection may drop. However, the amount of resources allocated toeach user can be controlled, with fewer resources allocated to delaytolerant applications such as e-mail. Certain 5G users will be runningdelay critical applications with their devices and will be paying for apremium service. These type of users should be prioritized indestination cell and resource allocations. Application, service and usercontext can be used to determine priority and the level of resourceallocations to 5G users.

Study of historical data on what a certain user does after getting offthe vehicle (or after getting on) will be useful to determine thecell/resource allocation. For example, after getting off, some usersstop viewing content and rapidly walk away. Some users stay on thestation for another bus/train and continue to view the content. Thiskind of differentiation helps to prioritize the cell and resourceallocations, and the type of cell (Macro or Small cell) the user shouldbe connected to.

The type of application which a user is running will have a significantimpact on the level of resource required. If a user in the vehicle isvideo streaming via the wireless communication network, he or sherequires a large amount of resources immediately after handover tocontinue with the same QoS. On the other hand, a user downloadinge-mails would not notice a few seconds delay, so the (bulk of) resourceallocation in the fixed cell can be held up while the resources becomeavailable after off-loading in the opposite direction (i.e., from fixedto moving cell).

For continuation of providing some popular content, D2D options may beavailable at the bus/train stop or the vehicle (in the oppositedirection flow). These kind of D2D ‘donor UEs’ can indicate theircontent store to the serving eNBs when camping on. This information canbe passed on to the controller and can be used as guidance to offloadsome transition users from the cellular resources.

FIG. 5 is a block diagram illustrating an example of a UE (terminal,mobile device) to which the present invention may be applied. The UE mayinclude any type of device which may be used in a wireless communicationsystem described above and may include cellular (or cell) phones(including smartphones), personal digital assistants (PDAs) with mobilecommunication capabilities, laptops or computer systems with mobilecommunication components. The UE includes transmitter/receiver unit(s)804 connected to at least one antenna 802 (together defining acommunication unit) and a controller 806 having access to memory in theform of a storage medium 808. The controller may be, for example, amicroprocessor, digital signal processor (DSP), ASIC, FPGA, or otherlogic circuitry programmed or otherwise configured to perform thevarious functions described above. For example, the various functionsdescribed above may be embodied in the form of a computer program storedin the storage medium 808 and executed by the controller 804. Thetransmission/reception unit 804 is arranged, under control of thecontroller 806, to perform functions such as receiving a handovercommand from an eNB and so forth as discussed previously.

FIG. 6 is a block diagram illustrating an example of an eNB 10, 11, 12or 13 to which the present invention may be applied. The eNB includestransmitter/receiver unit(s) 904 connected to at least one antenna 902(together defining a communication unit) and a controller 906. Thecontroller may be, for example, microprocessor, digital signal processor(DSP), ASIC, FPGA, or other logic circuitry programmed or otherwiseconfigured to perform various functions such as performing resourceallocation (under network control) for the UEs which it serves. Forexample, the various functions described above may be embodied in theform of a computer program stored in the storage medium 908 and executedby the controller 906. The transmission/reception unit 904 isresponsible for transmitting information such as data concerning UEs tothe central controller, receiving guidance from the central controllerconcerning handovers and resource allocation, and so forth.

Various modifications are possible within the scope of the presentinvention.

For simplicity, the above description has assumed that a user's commuteinvolves a single bus journey, but of course the principle of theinvention can be extended to journeys involving a number of publictransportation vehicles not necessarily of the same kind, for example atrain journey followed by a bus journey.

The “fixed cells” referred to above may include logical or virtualcells.

Any of the embodiments mentioned above may be combined in the samesystem. In any of the aspects or embodiments of the invention describedabove, the various features may be implemented in hardware, or assoftware modules running on one or more processors. Features of oneaspect may be applied to any of the other aspects.

The invention also provides a computer program or a computer programproduct for carrying out any of the methods described herein, and acomputer readable medium having stored thereon a program for carryingout any of the methods described herein.

A computer program embodying the invention may be stored on acomputer-readable medium, or it may, for example, be in the form of asignal such as a downloadable data signal provided from an Internetwebsite, or it may be in any other form.

INDUSTRIAL APPLICABILITY

The invention allows efficient handover of mobile users travelling inpublic transportation vehicles, and contributes to reducing the load ona wireless communication network as well as to improving the QoSprovided to users.

1. A wireless communication system using cells to provide wirelessaccess of users to services, comprising: a first base station installedon board a public transportation vehicle, to provide a moving cell; atleast one second base station installed at a stop at which users enteror leave the vehicle, to provide one or more fixed cells; and a centralcontroller for guiding handovers of users entering or leaving thevehicle; wherein the first and second base stations are arranged toprovide data concerning users to the central controller, and the centralcontroller is arranged to gather profile data of users based on the dataprovided by the base stations, make predictions about which users arelikely to enter and leave the vehicle at the stop, and based on thepredictions, to provide guidance to the first and second base stationsfor performing handovers of the users.
 2. The system according to claim1 wherein the central controller is arranged to gather the profile dataof users by recording details provided by the first and second basestations of wireless access of each user to the moving cell and/or fixedcells during a plurality of journeys using the public transportationvehicle.
 3. The system according to claim 2 wherein said detailsinclude: at least one identity of the user; a time at which the userestablished a connection with the moving or fixed cells; and a time atwhich the user ended the connection with the moving or fixed cells. 4.The system according to claim 3 wherein said details further include:information identifying a service or services which the moving or fixedcells provide to the user.
 5. The system according to claim 3 whereinthe identity of the user includes at least one of: an ID code assignedto the user by the wireless communication system; and an ID codecontained in a RFID device of the user.
 6. The system according to claim5 wherein said details further include: information identifying aservice or services which the moving or fixed cells provide to the user.7. The system according to claim 1 wherein the guidance provided by thecentral controller includes a predicted number of handovers which willbe needed from the moving cell to a fixed cell and from a fixed cell tothe moving cell when users enter and leave the vehicle at the stop. 8.The system according to claim 1 wherein the guidance provided by thecentral controller includes an indication of resources predicted to befreed up from the moving cell and the fixed cells as a result of thepredicted handovers.
 9. The system according to claim 1 wherein theguidance provided by the central controller includes at least one of: anindication of resource allocations predicted to be needed in the movingcell and the fixed cells after users have entered and left the vehicleat the stop; and an indication of which fixed cell will be selected asthe handover target cell for a user leaving the vehicle.
 10. The systemaccording to claim 9 wherein said details provided by the first andsecond base station include information identifying a service which themoving or a fixed cell provides to the user, the central controller isarranged to predict whether the user is likely to continue to requirewireless access to the service after leaving or entering the vehicle,and the indication of selected handover target cell and/or indication ofresource allocations takes into account resource demands of the service.11. The system according to claim 1 wherein the first base station isfurther arranged to update the central controller with the position ofthe public transportation vehicle and the central controller is arrangedto provide said guidance prior to the vehicle reaching the stop.
 12. Thesystem according to claim 1 wherein the first and second base stationsare arranged to perform the handovers without requiring said handoversto be triggered by measurement reports from the users.
 13. The systemaccording to claim 12 wherein the handovers are performed on the basisof one or more of: guidance from the central controller regarding whichusers are predicted to enter or leave the vehicle; recent handovers ofother users during the same journey of the vehicle; past handovers ofthe same user during earlier journeys on the vehicle; measurements ofthe fixed cell by the first base station; and historical measurementreports of the users.
 14. A central controller for wirelesscommunication system using cells to provide wireless access of users toservices, the wireless communication system comprising a first basestation installed on board a public transportation vehicle, to provide amoving cell and at least one second base station installed at a stop atwhich users enter or leave the vehicle, to provide one or more fixedcells; wherein the central controller is arranged to receive dataconcerning the users from at least the first base station, gatherprofile data of the users based on the data received, make predictionsabout which users are likely to enter and leave the vehicle at the stop,and based on the predictions, to provide guidance to the first andsecond base stations for performing handovers of the users.
 15. A methodof controlling a wireless communication system, the wirelesscommunication system using cells to provide wireless access of users toservices and comprising a first base station installed on board a publictransportation vehicle to provide a moving cell and at least one secondbase station installed at a stop at which users enter or leave thevehicle, to provide one or more fixed cells, wherein the methodcomprises steps of: receiving data concerning the users from at leastthe first base station; gathering profile data of the users based on thedata received; making predictions about which users are likely to enterand leave the vehicle at the stop, and based on the predictions,providing guidance to the first and second base stations for performinghandovers of the users.
 16. A non-transitory computer-readable mediumembodying software which, when executed by a general-purpose computerconnected to first and second base stations, causes the computer toprovide the central controller according to claim 14.